Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$18.32	10.428%	$20.2304	$20.23	$20.25	$20.20
Purchase #2	$56.95	10.244%	$62.784	$62.78	$62.80	$62.80
Purchase #3	$134.76	11.817%	$150.6846	$150.68	$150.70	$150.70
Purchase #4	$189.86	5.285%	$199.8941	$199.89	$199.90	$199.90
Purchase #5	$173.62	9.238%	$189.659	$189.66	$189.65	$189.70
Purchase #6	$54.87	8.548%	$59.5603	$59.56	$59.55	$59.60
Purchase #7	$220.87	13.593%	$250.8929	$250.89	$250.90	$250.90
7 purchase totals =	$849.25		$933.7053	$933.69	$933.75	$933.80